Publications by authors named "Colin L Masters"

566 Publications

No Influence of Age-Related Hearing Loss on Brain Amyloid-β.

J Alzheimers Dis 2021 Nov 18. Epub 2021 Nov 18.

Cogstate, Melbourne, Australia.

Background: Hearing loss is independently associated with a faster rate of cognitive decline in older adults and has been identified as a modifiable risk factor for dementia. The mechanism for this association is unknown, and there has been limited exploration of potential casual pathology.

Objective: Our objective was to investigate whether there was an association between degree of audiometrically measured hearing loss (HL) and brain amyloid-β (Aβ) in a pre-clinical sample.

Methods: Participants of the Australian Imaging and Biomarker Longitudinal Study (AIBL; n = 143) underwent positron emission tomography (PET) imaging and objective measurement of hearing thresholds within 5 years of imaging, as well as cognitive assessment within 2 years of imaging in this observational cohort study.

Results: With one exception, study participants who had cognitive assessments within 2 years of their PET imaging (n = 113) were classified as having normal cognition. There was no association between cognitive scores and degree of hearing loss, or between cognitive scores and Aβ load. No association between HL and Aβ load was found once age was controlled for. As previously reported, positive Apolipoprotein E4 (APOE4) carrier status increased the risk of being Aβ positive (p = 0.002).

Conclusion: Degree of HL was not associated with positive Aβ status.
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http://dx.doi.org/10.3233/JAD-215121DOI Listing
November 2021

Connecting Cohorts to Diminish Alzheimer's Disease (CONCORD-AD): A Report of an International Research Collaboration Network.

J Alzheimers Dis 2021 Nov 8. Epub 2021 Nov 8.

Department of Psychiatry, Alzheimer's Disease Research Center, Icahn School of Medicine at Mount Sinai, New York, NY, USA.

Longitudinal observational cohort studies are being conducted worldwide to understand cognition, biomarkers, and the health of the aging population better. Cross-cohort comparisons and networks of registries in Alzheimer's disease (AD) foster scientific exchange, generate insights, and contribute to the evolving clinical science in AD. A scientific working group was convened with invited investigators from established cohort studies in AD, in order to form a research collaboration network as a resource to address important research questions. The Connecting Cohorts to Diminish Alzheimer's Disease (CONCORD-AD) collaboration network was created to bring together global resources and expertise, to generate insights and improve understanding of the natural history of AD, to inform design of clinical trials in all disease stages, and to plan for optimal patient access to disease-modifying therapies once they become available. The network brings together expertise and data insights from 7 cohorts across Australia, Europe, and North America. Notably, the network includes populations recruited through memory clinics as well as population-based cohorts, representing observations from individuals across the AD spectrum. This report aims to introduce the CONCORD-AD network, providing an overview of the cohorts involved, reporting the common assessments used, and describing the key characteristics of the cohort populations. Cohort study designs and baseline population characteristics are compared, and available cognitive, functional, and neuropsychiatric symptom data, as well as the frequency of biomarker assessments, are summarized. Finally, the challenges and opportunities of cross-cohort studies in AD are discussed.
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http://dx.doi.org/10.3233/JAD-210525DOI Listing
November 2021

Effects of a physical activity intervention on brain atrophy in older adults at risk of dementia: a randomized controlled trial.

Brain Imaging Behav 2021 Nov 10. Epub 2021 Nov 10.

Department of Radiology, University of Melbourne, Melbourne, Australia.

Lack of physical activity is a risk factor for dementia, however, the utility of interventional physical activity programs as a protective measure against brain atrophy and cognitive decline is uncertain. Here we present the effect of a randomized controlled trial of a 24-month physical activity intervention on global and regional brain atrophy as characterized by longitudinal voxel-based morphometry with T1-weighted MRI images. The study sample consisted of 98 participants at risk of dementia, with mild cognitive impairment or subjective memory complaints, and having at least one vascular risk factor for dementia, randomized into an exercise group and a control group. Between 0 and 24 months, there was no significant difference detected between groups in the rate of change in global, or regional brain volumes.
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http://dx.doi.org/10.1007/s11682-021-00577-7DOI Listing
November 2021

Genomics of Alzheimer's disease implicates the innate and adaptive immune systems.

Cell Mol Life Sci 2021 Dec 27;78(23):7397-7426. Epub 2021 Oct 27.

The Florey Institute, The University of Melbourne, 30 Royal Parade, Parkville, VIC, 3052, Australia.

Alzheimer's disease (AD) is a chronic neurodegenerative disease characterised by cognitive impairment, behavioural alteration, and functional decline. Over 130 AD-associated susceptibility loci have been identified by genome-wide association studies (GWAS), while whole genome sequencing (WGS) and whole exome sequencing (WES) studies have identified AD-associated rare variants. These variants are enriched in APOE, TREM2, CR1, CD33, CLU, BIN1, CD2AP, PILRA, SCIMP, PICALM, SORL1, SPI1, RIN3, and more genes. Given that aging is the single largest risk factor for late-onset AD (LOAD), the accumulation of somatic mutations in the brain and blood of AD patients have also been explored. Collectively, these genetic findings implicate the role of innate and adaptive immunity in LOAD pathogenesis and suggest that a systemic failure of cell-mediated amyloid-β (Aβ) clearance contributes to AD onset and progression. AD-associated variants are particularly enriched in myeloid-specific regulatory regions, implying that AD risk variants are likely to perturbate the expression of myeloid-specific AD-associated genes to interfere Aβ clearance. Defective phagocytosis, endocytosis, and autophagy may drive Aβ accumulation, which may be related to naturally-occurring antibodies to Aβ (Nabs-Aβ) produced by adaptive responses. Passive immunisation is providing efficiency in clearing Aβ and slowing cognitive decline, such as aducanumab, donanemab, and lecanemab (ban2401). Causation of AD by impairment of the innate immunity and treatment using the tools of adaptive immunity is emerging as a new paradigm for AD, but immunotherapy that boosts the innate immune functions of myeloid cells is highly expected to modulate disease progression at asymptomatic stage.
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http://dx.doi.org/10.1007/s00018-021-03986-5DOI Listing
December 2021

A six-metabolite panel as potential blood-based biomarkers for Parkinson's disease.

NPJ Parkinsons Dis 2021 Oct 14;7(1):94. Epub 2021 Oct 14.

Department of Biochemistry, Emory University School of Medicine, Atlanta, GA, 30322, USA.

Characterisation and diagnosis of idiopathic Parkinson's disease (iPD) is a current challenge that hampers both clinical assessment and clinical trial development with the potential inclusion of non-PD cases. Here, we used a targeted mass spectrometry approach to quantify 38 metabolites extracted from the serum of 231 individuals. This cohort is currently one of the largest metabolomic studies including iPD patients, drug-naïve iPD, healthy controls and patients with Alzheimer's disease as a disease-specific control group. We identified six metabolites (3-hydroxykynurenine, aspartate, beta-alanine, homoserine, ornithine (Orn) and tyrosine) that are significantly altered between iPD patients and control participants. A multivariate model to predict iPD from controls had an area under the curve (AUC) of 0.905, with an accuracy of 86.2%. This panel of metabolites may serve as a potential prognostic or diagnostic assay for clinical trial prescreening, or for aiding in diagnosing pathological disease in the clinic.
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http://dx.doi.org/10.1038/s41531-021-00239-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8516864PMC
October 2021

Deep Generative Medical Image Harmonization for Improving Cross-Site Generalization in Deep Learning Predictors.

J Magn Reson Imaging 2021 Sep 25. Epub 2021 Sep 25.

Artificial Intelligence in Biomedical Imaging Lab, University of Pennsylvania, Philadelphia, Pennsylvania, USA.

Background: In the medical imaging domain, deep learning-based methods have yet to see widespread clinical adoption, in part due to limited generalization performance across different imaging devices and acquisition protocols. The deviation between estimated brain age and biological age is an established biomarker of brain health and such models may benefit from increased cross-site generalizability.

Purpose: To develop and evaluate a deep learning-based image harmonization method to improve cross-site generalizability of deep learning age prediction.

Study Type: Retrospective.

Population: Eight thousand eight hundred and seventy-six subjects from six sites. Harmonization models were trained using all subjects. Age prediction models were trained using 2739 subjects from a single site and tested using the remaining 6137 subjects from various other sites.

Field Strength/sequence: Brain imaging with magnetization prepared rapid acquisition with gradient echo or spoiled gradient echo sequences at 1.5 T and 3 T.

Assessment: StarGAN v2, was used to perform a canonical mapping from diverse datasets to a reference domain to reduce site-based variation while preserving semantic information. Generalization performance of deep learning age prediction was evaluated using harmonized, histogram matched, and unharmonized data.

Statistical Tests: Mean absolute error (MAE) and Pearson correlation between estimated age and biological age quantified the performance of the age prediction model.

Results: Our results indicated a substantial improvement in age prediction in out-of-sample data, with the overall MAE improving from 15.81 (±0.21) years to 11.86 (±0.11) with histogram matching to 7.21 (±0.22) years with generative adversarial network (GAN)-based harmonization. In the multisite case, across the 5 out-of-sample sites, MAE improved from 9.78 (±6.69) years to 7.74 (±3.03) years with histogram normalization to 5.32 (±4.07) years with GAN-based harmonization.

Data Conclusion: While further research is needed, GAN-based medical image harmonization appears to be a promising tool for improving cross-site deep learning generalization.

Level Of Evidence: 4 TECHNICAL EFFICACY: Stage 1.
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http://dx.doi.org/10.1002/jmri.27908DOI Listing
September 2021

The case for low-level BACE1 inhibition for the prevention of Alzheimer disease.

Nat Rev Neurol 2021 Nov 21;17(11):703-714. Epub 2021 Sep 21.

German Center for Neurodegenerative Diseases (DZNE), Munich, Germany.

Alzheimer disease (AD) is the most common cause of dementia in older individuals (>65 years) and has a long presymptomatic phase. Preventive therapies for AD are not yet available, and potential disease-modifying therapies targeting amyloid-β plaques in symptomatic stages of AD have only just been approved in the United States. Small-molecule inhibitors of β-site amyloid precursor protein (APP)-cleaving enzyme 1 (BACE1; also known as β-secretase 1) reduce the production of amyloid-β peptide and are among the most advanced drug candidates for AD. However, to date all phase II and phase III clinical trials of BACE inhibitors were either concluded without benefit or discontinued owing to futility or the occurrence of adverse effects. Adverse effects included early, mild cognitive impairment that was associated with all but one inhibitor; preliminary results suggest that the cognitive effects are non-progressive and reversible. These discontinuations have raised questions regarding the suitability of BACE1 as a drug target for AD. In this Perspective, we discuss the status of BACE inhibitors and suggest ways in which the results of the discontinued trials can inform the development of future clinical trials of BACE inhibitors and related secretase modulators as preventative therapies. We also propose a series of experiments that should be performed to inform 'go-no-go' decisions in future trials with BACE inhibitors and consider the possibility that low levels of BACE1 inhibition could avoid adverse effects while achieving efficacy for AD prevention.
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http://dx.doi.org/10.1038/s41582-021-00545-1DOI Listing
November 2021

Citrullination of Amyloid-β Peptides in Alzheimer's Disease.

ACS Chem Neurosci 2021 10 14;12(19):3719-3732. Epub 2021 Sep 14.

Florey Institute of Neuroscience and Mental Health, University of Melbourne, Melbourne, Victoria 3010, Australia.

Protein citrullination (deimination of arginine residue) is a well-known biomarker of inflammation. Elevated protein citrullination has been shown to colocalize with extracellular amyloid plaques in AD patient brains. Amyloid-β (Aβ) peptides which aggregate and accumulate in the plaques of Alzheimer's disease (AD) have sequential N-terminal truncations and multiple post-translational modifications (PTM) such as isomerization, pyroglutamate formation, phosphorylation, nitration, and dityrosine cross-linking. However, no conclusive biochemical evidence exists whether citrullinated Aβ is present in AD brains. In this study, using high-resolution mass spectrometry, we have identified citrullination of Aβ in sporadic and familial AD brains by characterizing the tandem mass spectra of endogenous N-truncated citrullinated Aβ peptides. Our quantitative estimations demonstrate that ∼ 35% of pyroglutamate3-Aβ pool was citrullinated in plaques in the sporadic AD temporal cortex and ∼ 22% in the detergent-insoluble frontal cortex fractions. Similarly, hypercitrullinated pyroglutamate3-Aβ (∼ 30%) was observed in both the detergent-soluble as well as insoluble Aβ pool in familial AD cases. Our results indicate that a common mechanism for citrullination of Aβ exists in both the sporadic and familial AD. We establish that citrullination of Aβ is a remarkably common PTM, closely associated with pyroglutamate3-Aβ formation and its accumulation in AD. This may have implications for Aβ toxicity, autoantigenicity of Aβ, and may be relevant for the design of diagnostic assays and therapeutic targeting.
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http://dx.doi.org/10.1021/acschemneuro.1c00474DOI Listing
October 2021

Diagnostic and prognostic plasma biomarkers for preclinical Alzheimer's disease.

Alzheimers Dement 2021 Sep 8. Epub 2021 Sep 8.

Department of Biomedical Sciences, Macquarie University, North Ryde, New South Wales, Australia.

Introduction: This study involved a parallel comparison of the diagnostic and longitudinal monitoring potential of plasma glial fibrillary acidic protein (GFAP), total tau (t-tau), phosphorylated tau (p-tau181 and p-tau231), and neurofilament light (NFL) in preclinical Alzheimer's disease (AD).

Methods: Plasma proteins were measured using Simoa assays in cognitively unimpaired older adults (CU), with either absence (Aβ-) or presence (Aβ+) of brain amyloidosis.

Results: Plasma GFAP, t-tau, p-tau181, and p-tau231 concentrations were higher in Aβ+ CU compared with Aβ- CU cross-sectionally. GFAP had the highest effect size and area under the curve (AUC) in differentiating between Aβ+ and Aβ- CU; however, no statistically significant differences were observed between the AUCs of GFAP, p-tau181, and p-tau231, but all were significantly higher than the AUC of NFL, and the AUC of GFAP was higher than the AUC of t-tau. The combination of a base model (BM), comprising the AD risk factors, age, sex, and apolipoprotein E gene (APOE) ε4 status with GFAP was observed to have a higher AUC (>90%) compared with the combination of BM with any of the other proteins investigated in the current study. Longitudinal analyses showed increased GFAP and p-tau181 in Aβ+ CU and increased NFL in Aβ- CU, over a 12-month duration. GFAP, p-tau181, p-tau231, and NFL showed significant correlations with cognition, whereas no significant correlations were observed with hippocampal volume.

Discussion: These findings highlight the diagnostic and longitudinal monitoring potential of GFAP and p-tau for preclinical AD.
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http://dx.doi.org/10.1002/alz.12447DOI Listing
September 2021

The Amyloid-β Pathway in Alzheimer's Disease.

Mol Psychiatry 2021 Aug 30. Epub 2021 Aug 30.

Eisai Inc., Neurology Business Group, Woodcliff Lake, NJ, USA.

Breakthroughs in molecular medicine have positioned the amyloid-β (Aβ) pathway at the center of Alzheimer's disease (AD) pathophysiology. While the detailed molecular mechanisms of the pathway and the spatial-temporal dynamics leading to synaptic failure, neurodegeneration, and clinical onset are still under intense investigation, the established biochemical alterations of the Aβ cycle remain the core biological hallmark of AD and are promising targets for the development of disease-modifying therapies. Here, we systematically review and update the vast state-of-the-art literature of Aβ science with evidence from basic research studies to human genetic and multi-modal biomarker investigations, which supports a crucial role of Aβ pathway dyshomeostasis in AD pathophysiological dynamics. We discuss the evidence highlighting a differentiated interaction of distinct Aβ species with other AD-related biological mechanisms, such as tau-mediated, neuroimmune and inflammatory changes, as well as a neurochemical imbalance. Through the lens of the latest development of multimodal in vivo biomarkers of AD, this cross-disciplinary review examines the compelling hypothesis- and data-driven rationale for Aβ-targeting therapeutic strategies in development for the early treatment of AD.
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http://dx.doi.org/10.1038/s41380-021-01249-0DOI Listing
August 2021

Polygenic score modifies risk for Alzheimer's disease in ε4 homozygotes at phenotypic extremes.

Alzheimers Dement (Amst) 2021 5;13(1):e12226. Epub 2021 Aug 5.

Department of Epidemiology and Preventive Medicine School of Public Health and Preventive Medicine Monash University Melbourne Australia.

Introduction: Diversity in cognition among apolipoprotein E () ε4 homozygotes can range from early-onset Alzheimer's disease (AD) to a lifetime with no symptoms.

Methods: We evaluated a phenotypic extreme polygenic risk score (PRS) for AD between cognitively healthy ε4 homozygotes aged ≥75 years (n = 213) and early-onset ε4 homozygote AD cases aged ≤65 years (n = 223) as an explanation for this diversity.

Results: The PRS for AD was significantly higher in ε4 homozygote AD cases compared to older cognitively healthy ε4/ε4 controls (odds ratio [OR] 8.39; confidence interval [CI] 2.0-35.2;  = .003). The difference in the same PRS between ε3/ε3 extremes was not as significant (OR 3.13; CI 0.98-9.92;  = .053) despite similar numbers and power. There was no statistical difference in an educational attainment PRS between these age extreme case-controls.

Discussion: A PRS for AD contributes to modified cognitive expression of the ε4/ε4 genotype at phenotypic extremes of risk.
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http://dx.doi.org/10.1002/dad2.12226DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8339682PMC
August 2021

Erratum to: Creutzfeldt-Jakob disease surveillance in Australia: update to 31 December 2020.

Commun Dis Intell (2018) 2021 Aug 9;45. Epub 2021 Aug 9.

Erratum to Commun Dis Intell (2018) 2021;45 (https://doi.org/10.33321/cdi.2021.45.38).
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http://dx.doi.org/10.33321/cdi.2021.45.40DOI Listing
August 2021

Fifteen Years of the Australian Imaging, Biomarkers and Lifestyle (AIBL) Study: Progress and Observations from 2,359 Older Adults Spanning the Spectrum from Cognitive Normality to Alzheimer's Disease.

J Alzheimers Dis Rep 2021 3;5(1):443-468. Epub 2021 Jun 3.

The Florey Institute, The University of Melbourne, Parkville, VIC, Australia.

Background: The Australian Imaging, Biomarkers and Lifestyle (AIBL) Study commenced in 2006 as a prospective study of 1,112 individuals (768 cognitively normal (CN), 133 with mild cognitive impairment (MCI), and 211 with Alzheimer's disease dementia (AD)) as an 'Inception cohort' who underwent detailed ssessments every 18 months. Over the past decade, an additional 1247 subjects have been added as an 'Enrichment cohort' (as of 10 April 2019).

Objective: Here we provide an overview of these Inception and Enrichment cohorts of more than 8,500 person-years of investigation.

Methods: Participants underwent reassessment every 18 months including comprehensive cognitive testing, neuroimaging (magnetic resonance imaging, MRI; positron emission tomography, PET), biofluid biomarkers and lifestyle evaluations.

Results: AIBL has made major contributions to the understanding of the natural history of AD, with cognitive and biological definitions of its three major stages: preclinical, prodromal and clinical. Early deployment of Aβ-amyloid and tau molecular PET imaging and the development of more sensitive and specific blood tests have facilitated the assessment of genetic and environmental factors which affect age at onset and rates of progression.

Conclusion: This fifteen-year study provides a large database of highly characterized individuals with longitudinal cognitive, imaging and lifestyle data and biofluid collections, to aid in the development of interventions to delay onset, prevent or treat AD. Harmonization with similar large longitudinal cohort studies is underway to further these aims.
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http://dx.doi.org/10.3233/ADR-210005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8293663PMC
June 2021

Comparing amyloid-β plaque burden with antemortem PiB PET in autosomal dominant and late-onset Alzheimer disease.

Acta Neuropathol 2021 10 28;142(4):689-706. Epub 2021 Jul 28.

Department of Pathology and Immunology, Washington University in St. Louis, St. Louis, MO, USA.

Pittsburgh compound B (PiB) radiotracer for positron emission tomography (PET) imaging can bind to different types of amyloid-β plaques and blood vessels (cerebral amyloid angiopathy). However, the relative contributions of different plaque subtypes (diffuse versus cored/compact) to in vivo PiB PET signal on a region-by-region basis are incompletely understood. Of particular interest is whether the same staging schemes for summarizing amyloid-β burden are appropriate for both late-onset and autosomal dominant forms of Alzheimer disease (LOAD and ADAD). Here, we compared antemortem PiB PET with follow-up postmortem estimation of amyloid-β burden using stereologic methods to estimate the relative area fraction of diffuse and cored/compact amyloid-β plaques across 16 brain regions in 15 individuals with ADAD and 14 individuals with LOAD. In ADAD, we found that PiB PET correlated with diffuse plaques in the frontal, parietal, temporal, and striatal regions commonly used to summarize amyloid-β burden in PiB PET, and correlated with both diffuse and cored/compact plaques in the occipital lobe and parahippocampal gyrus. In LOAD, we found that PiB PET correlated with both diffuse and cored/compact plaques in the anterior cingulate, frontal lobe (middle frontal gyrus), and parietal lobe, and showed additional correlations with diffuse plaque in the amygdala and occipital lobe, and with cored/compact plaque in the temporal lobe. Thus, commonly used PiB PET summary regions predominantly reflect diffuse plaque burden in ADAD and a mixture of diffuse and cored/compact plaque burden in LOAD. In direct comparisons of ADAD and LOAD, postmortem stereology identified much greater mean amyloid-β plaque burdens in ADAD versus LOAD across almost all brain regions studied. However, standard PiB PET did not recapitulate these stereologic findings, likely due to non-trivial amyloid-β plaque burdens in ADAD within the cerebellum and brainstem-commonly used reference regions in PiB PET. Our findings suggest that PiB PET summary regions correlate with amyloid-β plaque burden in both ADAD and LOAD; however, they might not be reliable in direct comparisons of regional amyloid-β plaque burden between the two forms of AD.
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http://dx.doi.org/10.1007/s00401-021-02342-yDOI Listing
October 2021

Creutzfeldt-Jakob disease surveillance in Australia: update to 31 December 2020.

Commun Dis Intell (2018) 2021 Jul 22;45. Epub 2021 Jul 22.

Department of Medicine, The University of Melbourne, Victoria, 3010, Australia.

Abstract: Nationwide surveillance of Creutzfeldt-Jakob disease and other human prion diseases is performed by the Australian National Creutzfeldt-Jakob Disease Registry (ANCJDR). National surveillance encompasses the period since 1 January 1970, with prospective surveillance occurring from 1 October 1993. Over this prospective surveillance period, considerable developments have occurred in pre-mortem diagnostics; in the delineation of new disease subtypes; and in a heightened awareness of prion diseases in healthcare settings. Surveillance practices of the ANCJDR have evolved and adapted accordingly. This report summarises the activities of the ANCJDR during 2020. Since the ANCJDR began offering diagnostic cerebrospinal fluid (CSF) 14-3-3 protein testing in Australia in September 1997, the annual number of referrals has steadily increased. In 2020, 510 domestic CSF specimens were referred for 14-3-3 protein testing and 85 persons with suspected human prion disease were formally added to the national register. As of 31 December 2020, just over half (44 cases) of the 85 suspect case notifications remain classified as 'incomplete'; 27 cases were excluded through either detailed clinical follow-up (9 cases) or neuropathological examination (18 cases); 18 cases were classified as 'definite' and eleven as 'probable' prion disease. For 2020, sixty percent of all suspected human-prion-disease-related deaths in Australia underwent neuropathological examination. No cases of variant or iatrogenic CJD were identified. The SARS-CoV-2 pandemic did not affect prion disease surveillance outcomes in Australia.
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http://dx.doi.org/10.33321/cdi.2021.45.38DOI Listing
July 2021

Comparison of CSF biomarkers in Down syndrome and autosomal dominant Alzheimer's disease: a cross-sectional study.

Lancet Neurol 2021 08;20(8):615-626

Department of Neurology, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA.

Background: Due to trisomy of chromosome 21 and the resultant extra copy of the amyloid precursor protein gene, nearly all adults with Down syndrome develop Alzheimer's disease pathology by the age of 40 years and are at high risk for dementia given their increased life expectancy compared with adults with Down syndrome in the past. We aimed to compare CSF biomarker patterns in Down syndrome with those of carriers of autosomal dominant Alzheimer's disease mutations to enhance our understanding of disease mechanisms in these two genetic groups at high risk for Alzheimer's disease.

Methods: We did a cross-sectional study using data from adults enrolled in the Alzheimer's Biomarker Consortium-Down Syndrome (ABC-DS) study, a multisite longitudinal study of Alzheimer's disease in Down syndrome, as well as a cohort of carriers of autosomal dominant Alzheimer's disease mutations and non-carrier sibling controls enrolled in the Dominantly Inherited Alzheimer Network (DIAN) study. For ABC-DS, participants with baseline CSF, available clinical diagnosis, and apolipoprotein E genotype as of Jan 31, 2019, were included in the analysis. DIAN participants with baseline CSF, available clinical diagnosis, and apolipoprotein E genotype as of June 30, 2018, were evaluated as comparator groups. CSF samples obtained from adults with Down syndrome, similarly aged carriers of autosomal dominant Alzheimer's disease mutations, and non-carrier siblings (aged 30-61 years) were analysed for markers of amyloid β (Aβ, Aβ); tau phosphorylated at threonine 181-related processes; neuronal, axonal, or synaptic injury (total tau, visinin-like protein 1, neurofilament light chain [NfL], synaptosomal-associated protein 25); and astrogliosis and neuroinflammation (chitinase-3-like protein 1 [YKL-40]) via immunoassay. Biomarker concentrations were compared as a function of dementia status (asymptomatic or symptomatic), and linear regression was used to evaluate and compare the relationship between biomarker concentrations and age among groups.

Findings: We assessed CSF samples from 341 individuals (178 [52%] women, 163 [48%] men, aged 30-61 years). Participants were adults with Down syndrome (n=41), similarly aged carriers of autosomal dominant Alzheimer's disease mutations (n=192), and non-carrier siblings (n=108). Individuals with Down syndrome had patterns of Alzheimer's disease-related CSF biomarkers remarkably similar to carriers of autosomal dominant Alzheimer's disease mutations, including reductions (all p<0·0080) in Aβ to Aβ ratio and increases in markers of phosphorylated tau-related processes; neuronal, axonal, and synaptic injury (p<0·080); and astrogliosis and neuroinflammation, with greater degrees of abnormality in individuals with dementia. Differences included overall higher concentrations of Aβ and YKL-40 (both p<0·0008) in Down syndrome and potential elevations in CSF tau (p<0·010) and NfL (p<0·0001) in the asymptomatic stage (ie, no dementia symptoms).

Funding: National Institute on Aging, Eunice Kennedy Shriver National Institute of Child Health and Human Development, German Center for Neurodegenerative Diseases, and Japan Agency for Medical Research and Development.
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http://dx.doi.org/10.1016/S1474-4422(21)00139-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8496347PMC
August 2021

Pattern and degree of individual brain atrophy predicts dementia onset in dominantly inherited Alzheimer's disease.

Alzheimers Dement (Amst) 2021 5;13(1):e12197. Epub 2021 Jul 5.

The Florey Institute University of Melbourne Parkville Victoria Australia.

Introduction: Asymptomatic and mildly symptomatic dominantly inherited Alzheimer's disease mutation carriers (DIAD-MC) are ideal candidates for preventative treatment trials aimed at delaying or preventing dementia onset. Brain atrophy is an early feature of DIAD-MC and could help predict risk for dementia during trial enrollment.

Methods: We created a dementia risk score by entering standardized gray-matter volumes from 231 DIAD-MC into a logistic regression to classify participants with and without dementia. The score's predictive utility was assessed using Cox models and receiver operating curves on a separate group of 65 DIAD-MC followed longitudinally.

Results: Our risk score separated asymptomatic versus demented DIAD-MC with 96.4% (standard error = 0.02) and predicted conversion to dementia at next visit (hazard ratio = 1.32, 95% confidence interval [CI: 1.15, 1.49]) and within 2 years (area under the curve = 90.3%, 95% CI [82.3%-98.2%]) and improved prediction beyond established methods based on familial age of onset.

Discussion: Individualized risk scores based on brain atrophy could be useful for establishing enrollment criteria and stratifying DIAD-MC participants for prevention trials.
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http://dx.doi.org/10.1002/dad2.12197DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8256623PMC
July 2021

A trial of gantenerumab or solanezumab in dominantly inherited Alzheimer's disease.

Nat Med 2021 Jul 21;27(7):1187-1196. Epub 2021 Jun 21.

University of Alabama at Birmingham School of Medicine, Birmingham, AL, USA.

Dominantly inherited Alzheimer's disease (DIAD) causes predictable biological changes decades before the onset of clinical symptoms, enabling testing of interventions in the asymptomatic and symptomatic stages to delay or slow disease progression. We conducted a randomized, placebo-controlled, multi-arm trial of gantenerumab or solanezumab in participants with DIAD across asymptomatic and symptomatic disease stages. Mutation carriers were assigned 3:1 to either drug or placebo and received treatment for 4-7 years. The primary outcome was a cognitive end point; secondary outcomes included clinical, cognitive, imaging and fluid biomarker measures. Fifty-two participants carrying a mutation were assigned to receive gantenerumab, 52 solanezumab and 40 placebo. Both drugs engaged their Aβ targets but neither demonstrated a beneficial effect on cognitive measures compared to controls. The solanezumab-treated group showed a greater cognitive decline on some measures and did not show benefits on downstream biomarkers. Gantenerumab significantly reduced amyloid plaques, cerebrospinal fluid total tau, and phospho-tau181 and attenuated increases of neurofilament light chain. Amyloid-related imaging abnormalities edema was observed in 19.2% (3 out of 11 were mildly symptomatic) of the gantenerumab group, 2.5% of the placebo group and 0% of the solanezumab group. Gantenerumab and solanezumab did not slow cognitive decline in symptomatic DIAD. The asymptomatic groups showed no cognitive decline; symptomatic participants had declined before reaching the target doses.
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http://dx.doi.org/10.1038/s41591-021-01369-8DOI Listing
July 2021

Alzheimer's disease research progress in Australia: The Alzheimer's Association International Conference Satellite Symposium in Sydney.

Alzheimers Dement 2021 May 31. Epub 2021 May 31.

Departments of Neuroscience and Neurology, Center for Translational Research in Neurodegenerative Disease, Normal Fixel Center for Neurological Diseases, University of Florida College of Medicine, Gainesville, Florida, USA.

The Alzheimer's Association International Conference held its sixth Satellite Symposium in Sydney, Australia in 2019, highlighting the leadership of Australian researchers in advancing the understanding of and treatment developments for Alzheimer's disease (AD) and other dementias. This leadership includes the Australian Imaging, Biomarker, and Lifestyle Flagship Study of Ageing (AIBL), which has fueled the identification and development of many biomarkers and novel therapeutics. Two multimodal lifestyle intervention studies have been launched in Australia; and Australian researchers have played leadership roles in other global studies in diverse populations. Australian researchers have also played an instrumental role in efforts to understand mechanisms underlying vascular contributions to cognitive impairment and dementia; and through the Women's Healthy Aging Project have elucidated hormonal and other factors that contribute to the increased risk of AD in women. Alleviating the behavioral and psychological symptoms of dementia has also been a strong research and clinical focus in Australia.
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http://dx.doi.org/10.1002/alz.12380DOI Listing
May 2021

Undetected Neurodegenerative Disease Biases Estimates of Cognitive Change in Older Adults.

Psychol Sci 2021 06 27;32(6):849-860. Epub 2021 May 27.

Charles F. and Joanne Knight Alzheimer Disease Research Center, Washington University in St. Louis.

Neurodegenerative disease is highly prevalent among older adults and, if undetected, may obscure estimates of cognitive change among aging samples. Our aim in this study was to determine the nature and magnitude of cognitive change in the absence of common neuropathologic markers of neurodegenerative disease. Cognitively normal older adults (ages 65-89 years, = 199) were classified as normal or abnormal using neuroimaging and cerebrospinal-fluid biomarkers of β-amyloid, tau, and neurodegeneration. When cognitive change was modeled without accounting for biomarker status, significant decline was evident for semantic memory, processing speed, and working memory. However, after adjusting for biomarker status, we found that the rate of change was attenuated and that the biomarker-normal group demonstrated no decline for any cognitive domain. These results indicate that estimates of cognitive change in otherwise healthy older adults will be biased toward decline when the presence of early neurodegenerative disease is not accounted for.
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http://dx.doi.org/10.1177/0956797620985518DOI Listing
June 2021

Characterization of brain-derived extracellular vesicle lipids in Alzheimer's disease.

J Extracell Vesicles 2021 05 11;10(7):e12089. Epub 2021 May 11.

The Florey Institute of Neuroscience and Mental Health The University of Melbourne Parkville Victoria Australia.

Lipid dyshomeostasis is associated with the most common form of dementia, Alzheimer's disease (AD). Substantial progress has been made in identifying positron emission tomography and cerebrospinal fluid biomarkers for AD, but they have limited use as front-line diagnostic tools. Extracellular vesicles (EVs) are released by all cells and contain a subset of their parental cell composition, including lipids. EVs are released from the brain into the periphery, providing a potential source of tissue and disease specific lipid biomarkers. However, the EV lipidome of the central nervous system is currently unknown and the potential of brain-derived EVs (BDEVs) to inform on lipid dyshomeostasis in AD remains unclear. The aim of this study was to reveal the lipid composition of BDEVs in human frontal cortex, and to determine whether BDEVs have an altered lipid profile in AD. Using semi-quantitative mass spectrometry, we describe the BDEV lipidome, covering four lipid categories, 17 lipid classes and 692 lipid molecules. BDEVs were enriched in glycerophosphoserine (PS) lipids, a characteristic of small EVs. Here we further report that BDEVs are enriched in ether-containing PS lipids, a finding that further establishes ether lipids as a feature of EVs. BDEVs in the AD frontal cortex offered improved detection of dysregulated lipids in AD over global lipid profiling of this brain region.  AD BDEVs had significantly altered glycerophospholipid and sphingolipid levels, specifically increased plasmalogen glycerophosphoethanolamine and decreased polyunsaturated fatty acyl containing lipids, and altered amide-linked acyl chain content in sphingomyelin and ceramide lipids relative to CTL. The most prominent alteration was a two-fold decrease in lipid species containing anti-inflammatory/pro-resolving docosahexaenoic acid. The in-depth lipidome analysis provided in this study highlights the advantage of EVs over more complex tissues for improved detection of dysregulated lipids that may serve as potential biomarkers in the periphery.
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http://dx.doi.org/10.1002/jev2.12089DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8111496PMC
May 2021

Bundle-specific associations between white matter microstructure and Aβ and tau pathology in preclinical Alzheimer's disease.

Elife 2021 05 13;10. Epub 2021 May 13.

Department of Psychiatry, Faculty of Medicine, McGill University, Montreal, Canada.

Beta-amyloid (Aβ) and tau proteins, the pathological hallmarks of Alzheimer's disease (AD), are believed to spread through connected regions of the brain. Combining diffusion imaging and positron emission tomography, we investigated associations between white matter microstructure specifically in bundles connecting regions where Aβ or tau accumulates and pathology. We focused on free-water-corrected diffusion measures in the anterior cingulum, posterior cingulum, and uncinate fasciculus in cognitively normal older adults at risk of sporadic AD and presymptomatic mutation carriers of autosomal dominant AD. In Aβ-positive or tau-positive groups, lower tissue fractional anisotropy and higher mean diffusivity related to greater Aβ and tau burden in both cohorts. Associations were found in the posterior cingulum and uncinate fasciculus in preclinical sporadic AD, and in the anterior and posterior cingulum in presymptomatic mutation carriers. These results suggest that microstructural alterations accompany pathological accumulation as early as the preclinical stage of both sporadic and autosomal dominant AD.
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http://dx.doi.org/10.7554/eLife.62929DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8169107PMC
May 2021

Deaths with Dementia in Indigenous and Non-Indigenous Australians: A Nationwide Study.

J Alzheimers Dis 2021 ;81(4):1589-1599

University of Queensland, School of Public Health, Faculty of Medicine, Brisbane, Queensland, Australia.

Background: The prevalence of dementia is generally reported to be higher among Indigenous peoples.

Objective: The rates and coding of dementia mortality were compared between Indigenous and non-Indigenous Australians.

Methods: De-identified individual records on causes of death for all people aged 40 years or more who died in Australia between 2006 and 2014 (n = 1,233,084) were used. There were 185,237 records with International Classification of Diseases, Tenth Revision, codes for dementia (Alzheimer's Disease, vascular dementia, or unspecified dementia) as the underlying cause of death or mentioned elsewhere on the death certificate. Death rates were compared using Poisson regression. Logistic regression was used to assess whether dementia was more likely to be classified as 'unspecified' type in Indigenous Australians.

Results: The rates of death with dementia were 57% higher in Indigenous Australians, compared to non-Indigenous, relative rate (RR) 1.57, 95% confidence interval (CI) (1.48, 1.66), p < 0.0001. This excess of deaths was highest at ages below 75 (RRs > 2, test for interaction p < 0.0001), and among men (test for interaction p < 0.0001). When the underreporting of Indigenous status on the death certificate was taken into account the relative rate increased to 2.17, 95% CI (2.07, 2.29). Indigenous Australians were also more likely to have their dementia coded as 'unspecified' on their death certificate (Odds Ratio 1.92, 95% CI (1.66, 2.21), p < 0.0001), compared to the non-Indigenous group.

Conclusion: This epidemiological analysis based on population level mortality data demonstrates the higher dementia-related mortality rate for Indigenous Australians especially at younger ages.
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http://dx.doi.org/10.3233/JAD-201175DOI Listing
September 2021

Longitudinal Trajectories in Cortical Thickness and Volume Atrophy: Superior Cognitive Performance Does Not Protect Against Brain Atrophy in Older Adults.

J Alzheimers Dis 2021 ;81(3):1039-1052

Centre of Excellence for Alzheimer's Disease Research & Care, School of Medical and Health Sciences, Edith Cowan University, Joondalup, Western Australia, Australia.

Background: Previous research has identified a small subgroup of older adults that maintain a high level of cognitive functioning well into advanced age. Investigation of those with superior cognitive performance (SCP) for their age is important, as age-related decline has previously been thought to be inevitable.

Objective: Preservation of cortical thickness and volume was evaluated in 76 older adults with SCP and 100 typical older adults (TOAs) assessed up to five times over six years.

Methods: Regions of interest (ROIs) found to have been associated with super-aging status (a construct similar to SCP status) in previous literature were investigated, followed by a discovery phase analyses of additional regions. SCPs were aged 70 + at baseline, scoring at/above normative memory (CVLT-II) levels for demographically similar individuals aged 30-44 years old, and in the unimpaired range for all other cognitive domains over the course of the study.

Results: In linear mixed models, following adjustment for multiple comparisons, there were no significant differences between rates of thinning or volume atrophy between SCPs and TOAs in previously identified ROIs, or the discovery phase analyses. With only amyloid-β negative individuals in the analyses, again there were no significant differences between SCPs and TOAs.

Conclusion: The increased methodological rigor in classifying groups, together with the influence of cognitive reserve, are discussed as potential factors accounting for our findings as compared to the extant literature on those with superior cognitive performance for their age.
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http://dx.doi.org/10.3233/JAD-201243DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8293653PMC
September 2021

Quantification of N-terminal amyloid-β isoforms reveals isomers are the most abundant form of the amyloid-β peptide in sporadic Alzheimer's disease.

Brain Commun 2021 9;3(2):fcab028. Epub 2021 Mar 9.

Florey Institute of Neuroscience and Mental Health, University of Melbourne, Melbourne, VIC 3010, Australia.

Plaques that characterize Alzheimer's disease accumulate over 20 years as a result of decreased clearance of amyloid-β peptides. Such long-lived peptides are subjected to multiple post-translational modifications, in particular isomerization. Using liquid chromatography ion mobility separations mass spectrometry, we characterized the most common isomerized amyloid-β peptides present in the temporal cortex of sporadic Alzheimer's disease brains. Quantitative assessment of amyloid-β N-terminus revealed that > 80% of aspartates (Asp-1 and Asp-7) in the N-terminus was isomerized, making isomerization the most dominant post-translational modification of amyloid-β in Alzheimer's disease brain. Total amyloid-β was ∼85% isomerized at Asp-1 and/or Asp-7 residues, with only 15% unmodified amyloid-β left in Alzheimer's disease. While amyloid-β the next most abundant N-terminus found in Alzheimer's disease brain, was only ∼50% isomerized at Asp-7 in Alzheimer's disease. Further investigations into different biochemically defined amyloid-β-pools indicated a distinct pattern of accumulation of extensively isomerized amyloid-β in the insoluble fibrillar plaque and membrane-associated pools, while the extent of isomerization was lower in peripheral membrane/vesicular and soluble pools. This pattern correlated with the accumulation of aggregation-prone amyloid-β in Alzheimer's disease brains. Isomerization significantly alters the structure of the amyloid-β peptide, which not only has implications for its degradation, but also for oligomer assembly, and the binding of therapeutic antibodies that directly target the N-terminus, where these modifications are located.
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http://dx.doi.org/10.1093/braincomms/fcab028DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8062259PMC
March 2021

Core Alzheimer's disease cerebrospinal fluid biomarker assays are not affected by aspiration or gravity drip extraction methods.

Alzheimers Res Ther 2021 04 16;13(1):79. Epub 2021 Apr 16.

Biomarkable, Ghent, Belgium.

Background: CSF biomarkers are well-established for routine clinical use, yet a paucity of comparative assessment exists regarding CSF extraction methods during lumbar puncture. Here, we compare in detail biomarker profiles in CSF extracted using either gravity drip or aspiration.

Methods: Biomarkers for β-amyloidopathy (Aβ1-42, Aβ1-40), tauopathy (total tau), or synapse pathology (BACE1, Neurogranin Trunc-p75, α-synuclein) were assessed between gravity or aspiration extraction methods in a sub-population of the Australian Imaging, Biomarkers and Lifestyle (AIBL) study (cognitively normal, N = 36; mild cognitive impairment, N = 8; Alzheimer's disease, N = 6).

Results: High biomarker concordance between extraction methods was seen (concordance correlation > 0.85). Passing Bablock regression defined low beta coefficients indicating high scalability.

Conclusions: Levels of these commonly assessed CSF biomarkers are not influenced by extraction method. Results of this study should be incorporated into new consensus guidelines for CSF collection, storage, and analysis of biomarkers.
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http://dx.doi.org/10.1186/s13195-021-00812-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8052760PMC
April 2021

Deficits in Monocyte Function in Age Related Macular Degeneration: A Novel Systemic Change Associated With the Disease.

Front Med (Lausanne) 2021 17;8:634177. Epub 2021 Mar 17.

Department of Anatomy and Neuroscience, The University of Melbourne, Melbourne, VIC, Australia.

Age-related macular degeneration (AMD) is characterized by the accumulation of debris in the posterior eye. In this study we evaluated peripheral blood monocyte phagocytic function at various stages of AMD and in aged matched control participants. Real-time tri-color flow cytometry was used to quantify phagocytic function of peripheral blood monocyte subsets (non-classic, intermediate and classic) isolated from subjects with intermediate or late AMD and compared with age matched healthy controls. Assessment of phagocytic function of monocytes isolated from those with and without reticular pseudodrusen was also made, and the effect of glatiramer acetate on phagocytic function assessed. Phagocytic function was reduced in all subjects with AMD, irrespective of stage of disease. However, there was no correlation between phagocytic function and drusen load, nor any difference between the level of phagocytosis in those with or without reticular pseudodrusen. Treatment with glatiramer acetate increased phagocytosis of classical and non-classical monocytes, normalizing the reduction in phagocytosis observed in those with AMD. These findings suggest that defective systemic phagocytosis is associated with both intermediate and late stages of AMD, highlighting a potential role in the accumulation of debris that occurs early in the disease process. Assessing peripheral monocyte phagocytic function provides further insights into the etiology of this disease and offer a novel therapeutic target.
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http://dx.doi.org/10.3389/fmed.2021.634177DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8010137PMC
March 2021

Plasma Amyloid-Beta Levels in a Pre-Symptomatic Dutch-Type Hereditary Cerebral Amyloid Angiopathy Pedigree: A Cross-Sectional and Longitudinal Investigation.

Int J Mol Sci 2021 Mar 13;22(6). Epub 2021 Mar 13.

Department of Biomedical Sciences, Macquarie University, North Ryde, NSW 2109, Australia.

Plasma amyloid-beta (Aβ) has long been investigated as a blood biomarker candidate for Cerebral Amyloid Angiopathy (CAA), however previous findings have been inconsistent which could be attributed to the use of less sensitive assays. This study investigates plasma Aβ alterations between pre-symptomatic Dutch-type hereditary CAA (D-CAA) mutation-carriers (MC) and non-carriers (NC) using two Aβ measurement platforms. Seventeen pre-symptomatic members of a D-CAA pedigree were assembled and followed up 3-4 years later (NC = 8; MC = 9). Plasma Aβ1-40 and Aβ1-42 were cross-sectionally and longitudinally analysed at baseline (T1) and follow-up (T2) and were found to be lower in MCs compared to NCs, cross-sectionally after adjusting for covariates, at both T1(Aβ1-40: = 0.001; Aβ1-42: = 0.0004) and T2 (Aβ1-40: = 0.001; Aβ1-42: = 0.016) employing the Single Molecule Array (Simoa) platform, however no significant differences were observed using the xMAP platform. Further, pairwise longitudinal analyses of plasma Aβ1-40 revealed decreased levels in MCs using data from the Simoa platform ( = 0.041) and pairwise longitudinal analyses of plasma Aβ1-42 revealed decreased levels in MCs using data from the xMAP platform ( = 0.041). Findings from the Simoa platform suggest that plasma Aβ may add value to a panel of biomarkers for the diagnosis of pre-symptomatic CAA, however, further validation studies in larger sample sets are required.
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http://dx.doi.org/10.3390/ijms22062931DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8000178PMC
March 2021

Is Associated with Amyloid-β and ε4-Related Cognitive Decline in Cognitively Normal Adults.

J Alzheimers Dis Rep 2021 Feb 24;5(1):111-120. Epub 2021 Feb 24.

Collaborative Genomics and Translation Group, Center for Precision Health, School of Medical and Health Sciences, Edith Cowan University, Joondalup, Western Australia, Australia.

.

Background: Genetic variation in Spondin-1, specifically rs11023139, has been associated with reduced rates of cognitive decline in individuals with Alzheimer's disease.

Objective: The aim of this study was to assess whether the association was present in cognitively normal older adults.

Methods: Longitudinal cognitive decline was investigated using linear mixed modelling in a cohort of 590 cognitively normal older adults enrolled in the Australian Imaging, Biomarkers and Lifestyle Study.

Results: No independent effect of Spondin-1 rs11023139 on cognitive decline was observed. However, significant associations were observed for the interaction between Apolipoprotein E 4 and rs11023139 in individuals with high amyloid-β burden. 4/rs11023139-A carriers declined significantly faster than 4/rs11023139-G_G carriers in measures of global cognition ( = 0.011) and verbal episodic memory ( = 0.020).

Conclusion: These results suggest that carriage of the Spondin-1 rs11023139-A allele significantly contributes to a worsening of cognitive performance in 4 cognitively normal older adults with a high neocortical amyloid-β burden.
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http://dx.doi.org/10.3233/ADR-200246DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7990462PMC
February 2021
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